The present invention generally relates to heat pump devices and more particularly, to an absorption type heat pump device.
Since energy consumed for air conditioning occupies a large portion of energy consumed by domestic and industrial appliances, there is a keen demand for development of technology for energy-saving air conditioning. Meanwhile, in response to diversification of energy sources, technology in which air conditioning is performed through direct utilization of heat energy without using electric power has been extensively studied. In this connection, absorption type heat pump devices have such advantages as silent operation, high reliability, long service life, etc. and therefore, attract wide attention.
An arrangement of a prior art absorption type heat pump device is shown in FIG. 1. The known absorption type heat pump device includes a generator 4, a condenser 6, an evaporator 8, and an absorber 1 which are connected in series to each other so as to form one cycle. Since there is a large difference in pressure between the generator 4 and the absorber 1 and weak solution having a large content of refrigerant is required to be fed from the absorber 1 at a lower pressure side to the generator 4 at a higher pressure side, a solution pump 2 is provided therebetween so as to feed a predetermined amount of the weak solution to the generator 4 at all times. In the generator 4, the weak solution is heated so as to emit refrigerant vapor therefrom such that strong solution having a reduced amount of the refrigerant is produced. The strong solution is returned to the absorber 1 through a pressure reducing valve 5 or a capillary. Meanwhile, the strong solution is heated to a high temperature, while the weak solution fed from the absorber 1 to the generator 4 is of a low temperature. Accordingly, a heat exchanger 3 is provided between the absorber 1 and the generator 4 such that sensible heat of the strong solution is transmitted to the weak solution.
More specifically, in the absorber 1, the strong solution returned from the generator 4 absorbs the refrigerant vapor carried from the evaporator 8 so as to be converted into the weak solution having a large content of the refrigerant. Heat produced at the time of the above described absorption is discarded or utilized as a heat source. The weak solution is pressurized by the solution pump 2 and then, heated by the heat exchanger 3 so as to be transported to the generator 4. In the generator 4, the refrigerant contained in the weak solution is generated in the state of vapor through external heating of the weak solution such that the weak solution is converted into the strong solution having a low content of the refrigerant. The strong solution is subjected to heat exchange with the weak solution at the heat exchanger 3 so as to be cooled, and then, reduced in pressure at the pressure reducing valve 5 so as to be returned to the absorber 1.
In the above described one cycle of the prior art absorption type heat pump device, the generator 4 is arranged to separate the refrigerant vapor produced therein and the strong solution having a low content of the refrigerant so as to discharge the refrigerant vapor and the strong solution to the condenser 6 and the absorber 1, respectively.
It is to be noted here that an inflow amount of the weak solution fed into the generator 4 is required to balance with an outflow amount of the refrigerant vapor and the strong solution, both discharged from the generator 4. Especially, in the case where the inflow amount of the weak solution exceeds the outflow amount of the refrigerant vapor and the strong solution, a whole space in the generator 4 is filled with the solution and finally, the strong solution is caused to flow into the condenser 6, thus seriously aggravating functions of the heat pump device. However, since an outflow amount of the strong solution discharged from the generator 4 has a complemental relation with an amount of the refrigerant vapor produced in the generator 4 with respect to a predetermined inflow amount of the weak solution flowing into the generator 4, the outflow amount of the strong solution varies with heating temperatures of the of the solution pump 2 cannot be maintained at a predetermined value. Accordingly, it becomes necessary to control the outflow amount of the strong solution such that the amount of the solution stored in the generator 4 is maintained at a predetermined value.
Especially, in the case where fluorohydrocarbon is used as the refrigerant, latent heat for evaporation of the refrigerant is small, so that the circulation amount of the solution becomes large and thus, the amount of the solution stored in the generator 4 varies considerably in response to even slight imbalance between the inflow amount of the weak solution and the outflow amount of the strong solution and the refrigerant vapor, thereby incurring a strong possibility that the solution flows into the condenser 6. Meanwhile, conventionally there have been employed large-sized generators of a type containing the solution to their full capacities. However, in the case where generators of a type in which the solution is caused to flow therethrough for improvement of the starting characteristics and making their sizes compact, the generator is reduced in volume, thus further increasing the above described possibility that the solution flows into the condenser 6.
Generally, in order to prevent the solution from flowing into the condenser 6, it has been so arranged that the solution in the generator 4 is maintained at a predetermined level. Firstly, a method of adjusting an opening of the pressure reducing valve 5 can be used for the level control of the solution. Namely, in the case where the level of the solution rises, the opening of the pressure reducing valve 5 is enlarged so as to increase the outflow amount of the strong solution. On the contrary, in the case where the level of the solution is lowered, the opening of the pressure reducing valve 5 is decreased so as to reduce the outflow amount of the strong solution.
Referring now to FIG. 2, there is shown a flow control device for the strong solution, employed in a known absorption type heat pump device. The known flow control device includes a float type level sensor 13 attached to the generator 4 such that the outflow amount of the strong solution is increased beyond a normal amount in the case where the solution exceeds a predetermined level. The weak solution flows into the generator 4 through a pipe 9 and then, is heated thereat by a heat source 10 such that the refrigerant vapor is generated from the weak solution. Subsequently, the refrigerant vapor is transported to the condenser 6 through a pipe 11. On the other hand, the strong solution is carried to the pressure reducing valve 5 through the heat exchanger 3 and then, discharged therefrom to the absorber 1 through a pipe 12. The float type level sensor 13 is arranged to detect the level of the solution such that the detection signals are converted into electrical signals and the like so as to adjust the opening of the pressure reducing valve 5. However, since the above described known flow control device includes a number of mechanical movable parts such as the float floating and sinking in the solution, the opening of the pressure reducing valve 5, thereby resulting in frequent malfunctions of the flow control device and higher production cost thereof.
Referring now to FIG. 3, there is shown another flow control device for the strong solution, employed in a prior art absorption type heat pump device. The prior art flow control device includes a suction pipe 21 for the generator 4 and having an inlet portion 21a formed with a plurality of pores such that an amount of the refrigerant vapor sucked into the inlet portion 21a varies according to levels of the solution in the generator 4. In the prior art flow control device, a fixed capillary 22 is used as the pressure reducing valve 5 in FIG. 1 such that dimensions of the capillary 22 is so selected as to correspond to a maximum permissible low resistance value. It should be noted that the maximum permissible flow resistance value means a flow resistance value assumbed by the capillary 22 at the time when the solution is maintained at a predetermined level without inflow of the refrigerant vapor into the suction pipe 21 even in the case where a difference in concentration between the weak solution and the strong solution becomes minimal due to temperature conditions, etc. with the result that the outflow amount of the strong solution to be returned to the absorber 1 is required to be increased or in the case where it becomes difficult to convey the strong solution from the generator 4 to the absorber 1 as a difference in pressure therebetween becomes small.
By the above described arrangement of the prior art flow control device of FIG. 3, in the case where the outflow amount of the strong solution is small or in the case where the strong solution is transported from the generator 4 to the absorber 1 smoothly due to increase of a difference in pressure therebetween, the level of the solution is lowered accordingly, so that the strong solution is caused to flow out of the generator 4, with the refrigerant vapor being mixed with the strong solution and thus, pressure loss of the strong solution becomes large, whereby the outflow amount of the strong solution is automatically controlled such that the solution is maintained substantially at the predetermined level.
Although the solution in the generator 4 can be easily and effectively maintained at the predetermined level by the prior art flow control device of FIG. 3, the prior art flow control device of FIG. 3 has such an inconvenience that, since an inside of the suction pipe 21 is subjected to supercooling at all times, the refrigerant vapor mixed with the strong solution is rapidly absorbed by the strong solution, so that a rather large amount of the refrigerant vapor is required to be mixed with the strong solution so as to sufficiently increase the pressure drop of the strong solution in the suction pipe 21 in the case where the outflow amount of the strong solution is small and thus, a large amount of the refrigerant vapor to be fed to the condenser 6 is required to be uselessly returned to the absorber 1, thereby resulting in a large reduction of an output of the heat pump device.